Technical aspects of oocyte cryopreservation

Since the successful development in the mouse, the oocyte cryopreservation has been applied with varying success to a number of different species incl uding the human. The recently reported successes in terms of pregnancies ob tained by human oocyte cryopreservation are encouraging. Several studies ty pically reported different rates of survival (20-80%), fertilization (30-60 %) and cleavage (32-100%). This variability of results throws some doubts o n the usefulness of oocyte cryopreservation in IVF treatment cycles. It rem ains to be determined whether the relatively different success rates report ed in literature, mainly in terms of survival rate, are due to methodologic al differences. We tried to investigate the effect of some factors on the o ocyte survival rate after thawing: the presence or absence of cumulus oopho rus and the exposure time of the oocytes to cryoprotectant. We suggest that a combination of several factors including both morphological and biophisi cal ones can affect the oocyte survival rate. (C) 2000 Published by Elsevie r Science Ireland Ltd. All rights reserved.